Solid-state imaging apparatus and imaging system

ABSTRACT

A solid-state imaging apparatus includes a pixel section in which a plurality of pixels are arranged in a matrix, a column signal line configured to output a pixel signal from the pixel section, a column amplifier circuit configured to invert and amplify the pixel signal, a bypass circuit configured to bypass the column amplifier circuit, an AD converter, and a control unit configured to change an operation mode of the AD converter in accordance with the operation of the bypass circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging apparatusincluding an AD conversion circuit and an imaging system.

2. Description of the Related Art

Some solid-state imaging apparatuses, for example MOS imagingapparatuses, are constituted by an imaging unit and column signalprocessing circuit, as described in Japanese Patent Laid-Open No.2008-167004. Japanese Patent Laid-Open No. 2008-167004 describes anarrangement in which a column amplifier circuit and an AD (Analogue toDigital) conversion circuit are mounted in the column signal processingcircuit, and AD conversion is performed for each column. This patentliterature document discloses a method of amplifying signals of aplurality of systems having different sensitivities, AD-converting them,and then combining them to enlarge the dynamic range without decreasingthe S/N ratio. Japanese Patent Laid-Open No. 2010-147614 describes atechnique of, in a still image shooting mode, turning on an amplifier toperform high-quality shooting, and in a moving image shooting mode for amonitor, turning off the amplifier to cause a pixel signal to bypass theamplifier, thereby reducing power.

Japanese Patent Laid-Open No. 2010-147614 discloses a technique ofswitching the input range of an AD converter when the amplifier isturned on/off, and more specifically, halving the amplitude of a rampwaveform and a counter operation when the amplifier is OFF.

SUMMARY OF THE INVENTION

The first aspect of the present invention provides a solid-state imagingapparatus comprising a pixel section in which a plurality of pixels arearranged in a matrix, a column signal line configured to output a pixelsignal from the pixel section, a column amplifier circuit configured toinvert and amplify the pixel signal, a bypass circuit configured tobypass the column amplifier circuit, an AD converter, and a control unitconfigured to change an operation mode of the AD converter, wherein theAD converter includes a ramp signal generation circuit configured togenerate a reference signal, a comparator configured to compare thereference signal and the pixel signal, and a counter configured to counta time, and output a count value corresponding to the time, and thecontrol unit is configured to: in a first operation mode, to control theAD converter to AD-convert the pixel signal from the column signal lineand bypass the column amplifier circuit by the bypass circuit, in asecond operation mode, to control the AD converter to AD-convert thepixel signal inverted and amplified by the column amplifier circuit, andto change one of a slope of a ramp signal and a counting procedure ofthe counter between the first operation mode and the second operationmode.

The second aspect of the present invention provides a solid-stateimaging apparatus comprising a pixel section in which a plurality ofpixels is arranged in a matrix, a column signal line configured tooutput a pixel signal from the pixel section, a column amplifier circuitconfigured to invert and amplify the pixel signal from the columnamplifier circuit, a bypass circuit configured to bypass the columnamplifier circuit, a successive approximation AD converter, a CDSprocessing unit configured to calculate a difference between an outputdigital value of a reset level from the AD converter, and an outputdigital value of an imaging signal obtained by photo-electricallyconverting light, and a control unit configured to change an operationmode of the AD converter, wherein the control unit is configured: in afirst operation mode, to control the AD converter to AD-convert thepixel signal from the column signal line and bypass the column amplifiercircuit by the bypass circuit, in a second operation mode, to controlthe AD converter to AD-convert an inverted/amplified output signal fromthe column amplifier circuit, and to change processing of the CDSprocessing unit between the first operation mode and the secondoperation mode.

The third aspect of the present invention provides an imaging systemcomprising above solid-state imaging apparatus; an optical systemconfigured to form an image on the solid-state imaging apparatus; and asignal processing circuit configured to process an output signal fromthe solid-state imaging apparatus.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram according to an embodiment;

FIG. 2 is a circuit diagram showing the circuit arrangement of a pixelsection;

FIG. 3 is a circuit diagram according to the first embodiment;

FIGS. 4A and 4B are timing charts exemplifying a driving methodaccording to the first embodiment;

FIG. 5 is a circuit diagram showing the circuit arrangement of a columnamplifier circuit;

FIG. 6 is a circuit diagram according to the second embodiment;

FIGS. 7A and 7B are timing charts exemplifying a driving methodaccording to the second embodiment;

FIG. 8 is a circuit diagram according to the third embodiment;

FIGS. 9A and 9B are timing charts exemplifying a driving methodaccording to the third embodiment; and

FIG. 10 is a block diagram showing an example of the arrangement of animaging system using an imaging apparatus.

DESCRIPTION OF THE EMBODIMENTS

The present invention provides a solid-state imaging apparatus whichperforms AD (Analogue to Digital) conversion operations respectivelycorresponding to a case in which an output from an amplifier configuredto perform inversion and amplification is AD-converted, and a case inwhich the amplifier is bypassed and an output is AD-converted.

In the solid-state imaging apparatus according to the present invention,a plurality of pixels for photo-electrically converting incident lightare arranged two-dimensionally in a matrix in a pixel section. Resettingand charge accumulation of a plurality of pixels are performed on a rowbasis. Outputs from the pixels are output to a column signal linearranged by column. Signals from pixels are read out to a column signalline by row. A column amplifier circuit which amplifies an analog signalfrom a pixel, and a column circuit which holds an amplified signal arearranged for each column signal line. By amplifying a pixel signal usingthe column amplifier circuit, the influence of noise generated in asubsequent circuit is reduced relatively to a pixel signal. This enableshigh-quality shooting at a high S/N ratio. Generally in a solid-stateimage sensor in which a column amplifier circuit and an AD converter aremounted, a total noise amount N_(Total) when the column amplifiercircuit amplifies a pixel signal by a gain of an absolute value “A” canbe represented by:N _(Total)=√{square root over (A·N _(Pix) ² +N _(amp(A)) ² +N _(ADC)²)}  (1)

where N_(Pix): random noise of a pixel;

N_(amp(A)): random noise generated in the column amplifier circuit whenthe gain of the column amplifier circuit is A and

N_(ADC): random noise generated in the AD converter. To simplify thedescription, the gain of the column amplifier circuit is simply A. Inequation (1), the random noise N_(amp(A)) of the column amplifiercircuit when the gain is A can be generally designed to be smaller thana value A·N_(amp(1)) obtained by amplifying, by A, random noiseN_(amp(1)) when the gain of the column amplifier circuit is 1. This isbecause the high-frequency (treble) cutoff frequency when the columnamplifier circuit has a high gain decreases.

When A=1, equation (1) is rewritten into:N _(Total)=√{square root over (N _(Pix) ² +N _(amp(1)) ² +N _(ADC)²)}  (2)

When the gain is 1, the column amplifier circuit need not perform signalamplification. Adversely, if the column amplifier circuit is used,random noise N_(amp(1)) is added to the total noise, as represented byequation (2), increasing the noise. Hence, when the column amplifiercircuit does not perform signal amplification, the use of the columnamplifier circuit increases noise, compared to the absence of the columnamplifier circuit.

First Embodiment

The first embodiment of the present invention will now be described indetail with reference to the accompanying drawings. FIG. 1 is a blockdiagram showing the first embodiment. In a pixel section 102, aplurality of pixels 101 are arranged in a matrix of N rows×M columns.The pixel 101 outputs an imaging signal based on incident light byphoto-electric conversion. FIG. 1 shows only some pixels 101. Columnsignal lines 103 output, by row, pixel signals from pixels selected by arow selection unit 104. Column amplifier circuits 105 receive the pixelsignals from the column signal lines 103. The column amplifier circuits105 invert and amplify the input pixel signals, and output the resultantsignals to AD conversion circuits 107. Bypass circuits 106 are circuitswhich cause pixel signals from the column signal lines 103 to bypass thecolumn amplifier circuits 105. A bypass control circuit 111 controlsbypassing of pixel signals. Setting circuits 108 are controlled by thebypass control circuit 111 to control an AD conversion operation. Acolumn selection circuit 113 sequentially transfers digital signalsprocessed by the setting circuits 108 to a digital output line 110. Adigital processing circuit 112 processes the digital signals transferredto the digital output line 110.

In this arrangement, according to the embodiment, for example, whenshooting is performed at a low gain such as the gain=1, AD conversion isexecuted in a first operation mode in which AD conversion is performedwithout amplifying a pixel signal from the column signal line 103. Whenshooting is performed at a high gain of the column amplifier circuit105, AD conversion is executed in a second operation mode in which apixel signal amplified by the column amplifier circuit is AD-converted.That is, whether or not to use the column amplifier circuit is selectedin accordance with the shooting condition. However, when the columnamplifier circuit is constructed by an inverting amplifier circuit, thepolarity of a signal and the operating point differ between the case inwhich the column amplifier circuit is used, and the case in which it isnot used. As a result, no appropriate AD conversion may be performed. Asa measure against this, the setting circuit 108 which controls the ADconversion operation is arranged to perform appropriate AD conversiondepending on whether the column amplifier circuit is bypassed. A settingcircuit 108 is included in each column in FIG. 1, but instead a singlesetting circuit may be included in the digital processing circuit 112 orthe AD conversion circuit 107.

An example of the circuit arrangement of the pixel 101 will be explainedwith reference to FIG. 2. A photodiode 152 is a photo-electric converterwhich converts incident light into charges by photo-electric conversion.The source of a transfer transistor 153 is electrically connected to thephotodiode 152, the gate is electrically connected to a transfer controlline 161, and the drain is electrically connected to a floatingdiffusion region (to be referred to as a FD region hereinafter) 154. TheFD region 154 is a region in which charges transferred from thephotodiode 152 via the transfer transistor 153 are held. The source of areset transistor 155 is electrically connected to the FD region 154, thegate is electrically connected to a reset control line 162, and thedrain is electrically connected to a power supply voltage. The gate ofan amplifier transistor 156 is electrically connected to the FD region154, the drain is electrically connected to the power supply voltage,and the source is electrically connected to a selecting transistor 157.The gate of the selecting transistor 157 is electrically connected to aselecting control line 163, the source is electrically connected to thecolumn signal line 103, and the drain is electrically connected to thesource of the amplifier transistor 156. The amplifier transistor 156amplifies a signal based on charges held in the FD region 154, andoutputs the amplified signal to the column signal line 103 via theselecting transistor 157. The reset control line 162, transfer controlline 161, and selecting control line 163 are electrically connected tothe row selection unit 104.

Next, the operation of the AD conversion circuit 107 will be explainedwith reference to FIG. 3. In FIG. 3, a description of parts denoted bythe same reference numerals as those in FIG. 1 will not be repeated. Acomparator 204 compares a voltage at the positive input terminal with areference signal input to the negative input terminal. The positiveinput terminal receives an output from the column amplifier circuit 105,or a pixel signal which is input from the column signal line 103 bybypassing the column amplifier circuit 105. When the voltage at thepositive input terminal is (equal to or) higher than that at thenegative input terminal, the comparator 204 outputs a High level (to bereferred to as H level hereinafter). When the voltage at the positiveinput terminal is lower than that at the negative input terminal, thecomparator 204 outputs a Low level (to be referred to as L levelhereinafter). The bypass circuit 106 is a circuit which causes a pixelsignal from the column signal line 103 to bypass the column amplifiercircuit 105. When an output 109 from the bypass control circuit 111 isat H level, the switch of the bypass circuit 106 is turned on to bypassthe column amplifier circuit 105 and short-circuit the column signalline 103 and the positive input terminal of the comparator 204. Inaddition, when the output 109 is at H level, the column amplifiercircuit 105 changes to, for example, an inactive state so as to nottransmit an output to the positive input terminal of the comparator 204.When the output 109 from the bypass control circuit 111 is at L level,the switch is turned off to input a pixel signal from the column signalline 103 to only the column amplifier circuit 105.

In the embodiment, the setting circuit 108 includes a ramp signalgeneration circuit 108-1 and latch memory circuit 108-2. The drivingmethods and processing methods of the ramp signal generation circuit108-1 and latch memory circuit 108-2 change in accordance with a signalfrom the bypass control circuit 111. In the embodiment, the ramp signalgeneration circuit 108-1 and latch memory circuit 108-2 are parts whichcompensate for a change of the polarity of a pixel signal and a shift ofthe operating point that occur between a case in which the columnamplifier circuit is used and a case in which it is not used. The rampsignal generation circuit 108-1 generates a ramp signal serving as areference signal. The ramp signal generation circuit 108-1 has afunction of changing the polarity of the slope of a ramp signal to begenerated with respect to the temporal change. The ramp signalgeneration circuit 108-1 changes the polarity of the slope of a rampsignal in accordance with a control signal from the bypass controlcircuit 111. The “polarity of the slope” of the ramp signal with respectto the temporal change means an increase or decrease in the signal levelof the ramp signal with respect to the lapse of time.

The latch memory circuit 108-2 is a memory circuit which latches andstores a count value 203 output from a counter 202 at the timing when anoutput from the comparator 204 is inverted. The latch memory circuit108-2 changes the timing to hold the count value 203, in correspondencewith a control signal from the bypass control circuit 111, based onwhether an output from the comparator 204 is inverted from H level to Llevel, or if it is inverted from L level to H level. A method of drivingthe solid-state imaging apparatus exemplified in FIGS. 2 and 3 will beexplained with reference to timing charts shown in FIGS. 4A and 4B. Inthe description of the circuit of FIG. 2, the source electrode and drainelectrode of a MOS transistor are electrically connected when the Hlevel is applied to the gate electrode, and are electricallydisconnected when the L level is applied to the gate electrode. If a MOStransistor of a type in which the source electrode and drain electrodeare electrically connected when a L-level pulse is applied to the gateelectrode is used, the same operation as that in the embodiment can beperformed by reversing the H and L levels of pulses shown in FIGS. 4Aand 4B.

FIG. 4A is a timing chart when the column amplifier circuit is bypassed.FIG. 4B is a timing chart when the column amplifier circuit is used toamplify a signal. In FIGS. 4A and 4B, PSEL, PTX, and PRES represent thestates of the selecting control line 163, transfer control line 161, andreset control line 162, respectively. An operation in the method ofdriving the solid-state imaging apparatus according to the embodimentwill be explained in detail sequentially from time t0 with reference tothe timing charts of FIGS. 4A and 4B.

First, an example when a signal from a pixel bypasses the columnamplifier circuit 105 will be described with reference to FIG. 4A. FIG.5 is a circuit diagram showing the column amplifier circuit 105. Forreference, the bypass circuit 106 is also illustrated. The columnamplifier circuit 105 is constituted by an inverting amplificationsource-grounded circuit. The column amplifier circuit 105 inverts andamplifies a signal input to an input terminal 502, and outputs theresultant signal from an output terminal 503. At time to, an output V109from the bypass control circuit 111 changes to H level to disconnect(turn off) a MOS transistor series-connected to a source-groundedamplifier MOS transistor. At this time, the switch of the bypass circuit106 is turned on. A pixel signal from the column signal line 103 appearsat the output terminal 503 from the input terminal 502, and is input tothe positive input terminal of the comparator 204. A switch PCOR is aswitch for resetting a capacitive element. In the timing of the timingchart shown in FIG. 4A, the switch PCOR keeps ON from time t0 to timet2, and in a subsequent period, keeps OFF (not shown). The switch PCORmay suffice to be turned off after time t1 and before time t2.

At time t0, the selecting control line PSEL for selecting a rowsubjected to readout in the pixel section changes to H level to turn onthe selecting transistor 157 and select a readout row. Also, the resetcontrol line changes to H level to turn on the reset transistor 155 andreset the FD region 154. Next, at time t1, the reset control linechanges from H level to L level to turn off the reset transistor 155 andhold the FD region 154 at the reset level. In response to this, avoltage V103 of the column signal line 103 changes to the reset level attime t1. An output from the column signal line 103 is stabilized by timet2, so AD conversion of the reset level starts from time t2.

At this time, in FIG. 4A, the output voltage V109 of the output 109 fromthe bypass control circuit 111 is at H level, and the column amplifiercircuit is bypassed. Hence, a voltage V204+ of the positive inputterminal of the comparator 204 changes to the reset level of V103. InFIG. 4A, in correspondence with a signal from the bypass control circuit111, the slope of a ramp signal generated by the ramp signal generationcircuit 108-1 has a negative polarity at which a voltage V204− decreasesover time from time t2. Simultaneously when a ramp signal is generated,the counter 202 starts counting and a counter value D203 changes. Atemporal change of the counter value is schematically shown as D203.When the magnitude relationship between the voltage V204− and thevoltage V204+ is reversed at time t3, an output V204o from thecomparator is inverted, and the latch memory circuit 108-2 holds acounter value at this time. The held value is the AD conversion resultof the reset level. The AD conversion of the reset level ends at t4, andthe ramp signal changes to an initial value.

Then, at t5, PTX changes to H level to turn on the transfer transistor153 and transfer charges generated in the photodiode 152 to the FDregion 154. At time t6 at which the signal level is stabilized, PTXchanges to L level to end the transfer. The transferred charges areconverted into an imaging signal, and the imaging signal is output tothe column signal line 103. Hence, a voltage V204+ of the positive inputterminal of the comparator 204 changes to the imaging signal level ofV103. At time t7, AD conversion of the imaging signal starts. At timet8, an output from the comparator 204 is inverted, and the counter valueD203 at this time is held as the AD conversion result of the signallevel in the latch memory circuit 108-2. A difference A (shown at theright end of D203 in FIG. 4A) between the held value of the reset leveland the held value of the imaging signal serves as an AD conversionresult having undergone CDS (Correlated Double Sampling) processing.This differential processing may be performed by the latch memorycircuit 108-2 or the digital processing circuit 112. Since a ramp signalis generated with a negative slope with respect to the reset level, thereset level can be AD-converted within a short time. The time taken forAD conversion of the reset level is shorter than the time taken for ADconversion of the imaging signal. Thus, the ramp signal generation timewhen the reset level is AD-converted can be shortened.

Next, an example in which an output from the column amplifier circuit isAD-converted will be explained with reference to FIG. 4B. Note that adescription of the same operation as that in FIG. 4A will not berepeated. In this case, the output 109 from the bypass control circuit111 is at L level, the switch of the bypass circuit 106 is turned off,and the column amplifier circuit 105 operates to invert and amplify apixel signal from the column signal line 103. The polarity of theinverted/amplified signal output from the column amplifier circuit isopposite to that in FIG. 4A. The bypass control circuit 111 controls theramp signal generation circuit 108-1 to generate a ramp signal with aslope opposite to that in the case of FIG. 4A.

The ramp signal generation circuit 108-1 starts generating a ramp signalwhose polarity of the slope temporally changes in the positive directionfrom time t2. The generated ramp signal is input to the negative inputterminal of the comparator 204. At this time, a reset-level voltageamplified by the column amplifier circuit 105 is input to the positiveinput terminal of the comparator 204. At time t3, an output from thecomparator 204 is inverted at the timing when the magnitude relationshipbetween the input voltage V204− and the input voltage V204+ is reversedat time t3. The latch memory circuit 108-2 holds a counter value at thistime as the reset level. After that, an output obtained by amplifying animaging signal by the column amplifier circuit 105 is similarlyAD-converted. The latch memory circuit 108-2 holds a counter value atthe timing of t8.

As described above, in FIG. 4A, a counter value is held when acomparator output V204o is inverted from H level to L level. Conversely,at the timing in FIG. 4B, a counter value is held when a comparatoroutput V204o is inverted from L level to H level. In FIG. 4B, an ADconversion output having undergone CDS processing can be obtained as adifference B (shown at the right end of D203 in FIG. 4B) between the ADconversion result of the reset level and the AD conversion result of theimaging signal. In the embodiment, as is apparent from FIGS. 4A and 4B,a signal B obtained by AD-converting a signal amplified by the columnamplifier circuit 105 is almost two times larger than a signal A whichhas been AD-converted without amplification. This is because a signalfrom a pixel is amplified by the gain of the column amplifier circuit105. The amplification factor is not limited to two times. In theembodiment, the setting circuit 108 controls, in accordance with theoutput 109 from the bypass control circuit 111, the polarity of theslope of the ramp signal, and latching when the output of comparator 204changes from H level to L level or when it changes from L level to Hlevel. Control by the setting circuit 108 based on the output 109 fromthe bypass control circuit 111 is not limited to this.

In the embodiment, the polarity of an input signal to the comparator 204is reversed depending on whether the column amplifier circuit isbypassed. The polarity of the ramp signal is changed to increase theprocessing efficiency when performing CDS processing. In the embodiment,an increase in the time taken for AD conversion of the reset level issuppressed by switching a temporal change of the polarity of the slopeof the ramp signal between the positive direction and the negativedirection by the ramp signal generation circuit 108-1.

From the relationship between equations (1) and (2), when the gain isalmost 1, the influence of noise can be reduced by bypassing the columnamplifier circuit and digitally obtaining a gain. For example, when thegain of the column amplifier circuit is 4.4 or 2.2, a column amplifieris used. When the gain is set to 1.1, the column amplifier is bypassedto perform AD conversion, and the gain of 1.1 is digitally obtained. Achange of the AD conversion operation is performed by the settingcircuit 108 by column in the embodiment, but may be performed by thedigital processing circuit 112.

Second Embodiment

FIG. 6 is an exemplary circuit diagram according to the secondembodiment. FIGS. 7A and 7B are timing charts according to the secondembodiment. In FIGS. 6, 7A, and 7B, the same reference numerals as thosein FIGS. 3, 4A, and 4B denote common parts, and a description thereofwill not be repeated. A ramp signal generation circuit 301 generates aramp signal. In the description of the second embodiment, the polarityof the slope of the ramp signal is not changed. The second embodimentwill be explained with reference to FIGS. 6, 7A, and 7B. A clockgenerator 302 generates a clock, and the generated clock is supplied toa setting circuit 108. The setting circuit 108 includes an up/downcounter. The counting procedures of the up/down counter are changed insynchronism with control of a bypass control circuit 111. The operationof a counter in a period from t2 to t3 and a period from t7 to t8 ischanged depending on which of counting-up and counting-down is performedby the up/down counter for counting. The period from t2 to t3 is aperiod in which AD conversion of the reset level is performed. Theperiod from t7 to t8 is a period in which AD conversion of the imagingsignal is performed.

An operation when a column amplifier circuit 105 is bypassed will bedescribed first with reference to FIG. 7A. First, the up/down counterperforms AD conversion of the reset level. The up/down counter startscounting-up at time t2, and stops the counting at timing t3 when a rampsignal V204− exceeds a reset level V204+ and a comparator 204 outputs aninverted output. Then, AD conversion of the imaging signal is performedfrom time t7. The up/down counter changes counting-up to counting-downto perform counting, and stops the counting at time t8. As a result, acount value A (shown at the right end of D203 in FIG. 7A) obtained bythe up/down counter reflects the difference between the imaging signaland the reset level. That is, the count value of the up/down counterreflects the result of AD conversion of the imaging signal havingundergone CDS processing.

Next, a case in which the column amplifier circuit 105 amplifies a pixelsignal will be explained with reference to FIG. 7B. In the embodiment,first, the reset level is AD-converted by counting-down (from t2 to t3).Thereafter, a pixel signal amplified by the column amplifier circuit iscounted up (from t7 to t8). By controlling counting-up and counting-downof the up/down counter in this manner, the influence of inversion andamplification of the pixel signal by the column amplifier circuit istaken into consideration. Therefore, an AD conversion result reflectingthe result of CDS processing can be obtained as a count value B (shownat the right end of D203 in FIG. 7B). In the embodiment, AD conversionis performed by controlling the counting direction of the up/downcounter without changing the polarity of the slope of the ramp signal.However, a change of the polarity of the slope of the ramp signal and achange of the counting direction of the up/down counter may be combinedin accordance with bypass control of the column amplifier circuit. Forexample, an increase in the time taken for AD conversion of the resetlevel can be suppressed by changing the slope of the ramp signal to benegative, and performing AD conversion, as shown in FIG. 4A. In thiscase, the up/down counter first counts the reset level by counting-down,and then counts the signal level by counting-up, obtaining an ADconversion result as the count value. In the embodiment, the order ofcounting-up and counting-down of the up/down counter is changed betweenthe first operation mode and the second operation mode.

Third Embodiment

Next, an embodiment of a successive approximation AD converter will bedescribed with reference to FIGS. 8, 9A, and 9B. In FIGS. 8, 9A, and 9B,the same reference numerals as those in FIGS. 3, 4A, and 4B denotecommon parts, and a description thereof will not be repeated. Also, adescription of parts having the same operations as those in the otherembodiments will not be repeated. The successive approximation ADconverter includes comparators 204, and binary weight capacitors,capacitance value C to 8C each connected to the negative input terminalof the corresponding comparator 204. The other terminal of each of thebinary weight capacitors, capacitance value C to 8C is connected to aswitch which switches between the ground voltage and the REF voltage.The switch is controlled by a control means. The binary weightcapacitors, capacitance value C to 8C, the switches, and the comparators204 form the successive approximation AD converter. The output of eachcomparator 204 is connected to a corresponding setting circuit 108. Thecomparator 204 compares a voltage at the positive input terminal with avoltage at the negative input terminal. The comparator 204 outputs Hlevel when the voltage at the positive input terminal is higher thanthat at the negative input terminal, and L level when the voltage at thepositive input terminal is lower than that at the negative inputterminal. First, a case in which a column amplifier circuit 105 isbypassed will be described with reference to FIG. 9A. At time t1 to timet5, AD conversion of the reset level is performed. Every time the switchselects the binary weight capacitor, the successive approximation ADconverter compares voltages at the input terminals of the comparator204, and stores the obtained comparison result in the setting circuit108. An imaging signal is transferred from time t6. After the level ofthe imaging signal is stabilized, AD conversion of the imaging signalstarts, and the AD conversion is performed from t7 to t11. Thedifference between the AD conversion result of the imaging signal andthe AD conversion result of the reset level is calculated, obtaining anAD conversion result after CDS processing. The output digital value ofthe AD conversion result of the reset level at the timing in FIG. 9Abecomes 1110=14, and the output digital value of the AD conversionresult of the imaging signal becomes 1100=12. The CDS processing unit ofthe setting circuit 108 performs differential processing, obtaining14−12=2 as the AD conversion output of the imaging signal. To thecontrary, in the case of FIG. 9B in which an output from the columnamplifier circuit 105 is AD-converted, the output digital value of ADconversion of the reset level becomes 0001=1, and the output digitalvalue of AD conversion of the signal level becomes 0101=5. The CDSprocessing unit performs differential processing between the reset leveland the signal level, obtaining 5−1=4 as the AD conversion outputresult.

Based on an output signal from a bypass control circuit 111, the settingcircuit 108 changes the differential processing of the AD conversionprocessing circuit to subtraction of the signal level from the resetlevel, or subtraction of the reset level from the signal level. A changeof the differential processing is performed by the setting circuit 108in the embodiment, but may be performed by a digital processing circuit112.

Further, the embodiment has employed the successive approximation ADconverter, but the AD conversion method is not limited to this. Forexample, a hybrid method of two AD conversion methods using a ΣΔ ADconverter and cyclic comparison AD converter may be adopted. In thiscase, when performing both AD conversion of the reset level and ADconversion of the signal level to calculate a difference, differentialprocessing can be properly performed by changing processing after ADconversion or the AD conversion method depending on the presence/absenceof bypassing of the column amplifier circuit.

Fourth Embodiment

FIG. 10 is a block diagram showing an example of the arrangement of animaging system according to the fourth embodiment of the presentinvention. An imaging system 800 includes, for example, an optical unit810, imaging apparatus 100, signal processing unit 830,recording/communication unit 840, timing control unit 850, systemcontrol unit 860, and playback/display unit 870. An imaging unit 820includes the imaging apparatus 100 and video signal processing unit 830.As the imaging apparatus 100, the solid-state imaging apparatusdescribed in each of the above embodiments is used.

The optical unit 810 serving as an optical system, such as a lens, formsan image by forming light traveling from an object into an image on apixel section 102 of the imaging apparatus 100 in which a plurality ofpixels are two-dimensionally arrayed. At a timing based on a signal fromthe timing control unit 850, the imaging apparatus 100 outputs a signalcorresponding to the light formed into an image on the pixel section102. The signal output from the imaging apparatus 100 is input to thesignal processing unit 830, and the signal processing unit 830 performssignal processing according to a method defined by a program or thelike. The signal obtained by processing by the signal processing unit830 is sent as image data to the recording/communication unit 840. Therecording/communication unit 840 sends, to the playback/display unit870, a signal for forming an image, and causes the playback/display unit870 to play back and display a moving image or still image. Also, therecording/communication unit 840 communicates with the system controlunit 860 in response to a signal received from the video signalprocessing unit 830. In addition, the recording/communication unit 840performs an operation of recording, on a recording medium (not shown), asignal for forming an image.

The system control unit 860 performs centralized control of theoperation of the imaging system, and controls driving of the opticalunit 810, timing control unit 850, recording/communication unit 840, andplayback/display unit 870. The system control unit 860 includes astorage device (not shown) serving as, for example, a recording medium,on which a program or the like necessary to control the operation of theimaging system is recorded. The system control unit 860 supplies, intothe imaging system, a signal for switching the driving mode inaccordance with, for example, a user operation. Examples are a change ofa readout row or a row to be reset, a change of the angle of view alongwith electronic zooming, and a shift of the angle of view along withelectronic image stabilization. The timing control unit 850 controls thedriving timings of the imaging apparatus 100 and signal processing unit830 under the control of the system control unit 860.

Other Embodiments

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-192366, filed Sep. 17, 2013, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A solid-state imaging apparatus comprising: apixel section in which a plurality of pixels are arranged in a matrix; acolumn signal line configured to output a pixel signal from the pixelsection; a column amplifier circuit configured to output an amplifiedsignal by inverting and amplifying the pixel signal; a bypass circuitconfigured to bypass the column amplifier circuit; an analogue todigital (AD) converter; and a control unit configured to change anoperation mode of the AD converter, wherein the AD converter includes aramp signal generation circuit configured to generate a referencesignal, a comparator configured to compare the reference signal and oneof the pixel signal and the amplified signal, and a counter configuredto count a time and output a count value corresponding to the time, andthe control unit is configured: in a first operation mode, to controlthe AD converter to AD-convert the pixel signal output from the columnsignal line via the bypass circuit, in a second operation mode, tocontrol the AD converter to AD-convert the amplified signal, and tochange one of a slope of a reference signal and a counting procedure ofthe counter between the first operation mode and the second operationmode.
 2. The solid-state imaging apparatus according to claim 1, whereina polarity of the slope of the reference signal is changed.
 3. Thesolid-state imaging apparatus according to claim 1, wherein the countingprocedure of the counter includes counting-up and counting-down.
 4. Thesolid-state imaging apparatus according to claim 1, wherein the ADconverter AD-converts a signal of a reset level of the pixel, and animaging signal obtained by photo-electrically converting light.
 5. Thesolid-state imaging apparatus according to claim 1, wherein the ADconverter AD-converts a signal based on a reset level of the pixelsignal, and an imaging signal obtained by photo-electrically convertinglight, and when the signal based on the reset level and the imagingsignal are AD-converted, a polarity of the slope of the ramp signal ischanged.
 6. The solid-state imaging apparatus according to claim 1,wherein the AD converter AD-converts a signal based on a reset level ofthe pixel signal, and an imaging signal obtained by photo-electricallyconverting light, and when the signal based on the reset level and theimaging signal are AD-converted, an order to perform counting-up andcounting-down of the counter is changed.
 7. The solid-state imagingapparatus according to claim 1, wherein the control unit controls thebypass circuit to cause the pixel signal from the column signal line tobypass the column amplifier circuit.
 8. An imaging system comprising: asolid-state imaging apparatus; an optical system configured to form animage on the solid-state imaging apparatus; and a signal processingcircuit configured to process an output signal from the solid-stateimaging apparatus, the solid-state imaging apparatus comprising: a pixelsection in which a plurality of pixels are arranged in a matrix; acolumn signal line configured to output a pixel signal from the pixelsection; a column amplifier circuit configured to output an amplifiedsignal by inverting and amplifying the pixel signal; a bypass circuitconfigured to bypass the column amplifier circuit; an analogue todigital (AD) converter; and a control unit configured to change anoperation mode of the AD converter, wherein the AD converter includes aramp signal generation circuit configured to generate a referencesignal, a comparator configured to compare the reference signal and oneof the pixel signal and the amplified signal, and a counter configuredto count a time and output a count value corresponding to the time, andthe control unit is configured: in a first operation mode, to controlthe AD converter to AD-convert the pixel signal output from the columnsignal line via the bypass circuit, in a second operation mode, tocontrol the AD converter to AD-convert the amplified signal, and tochange one of a slope of a reference signal and a counting procedure ofthe counter between the first operation mode and the second operationmode.